(1) Field of the Invention
The present invention relates to a sheet inverting device for use in copiers and printers with an automatic duplex printing function, and in particular to a device for inverting the face of the sheet with one side printed.
(2) Description of the Prior Art
As an example of a sheet inverting device used in conventional copiers with an automatic duplex printing function, a configuration shown in FIG. 1 was disclosed in Japanese Patent Publication Sho 61 No.23,146. In this figure, a first roller or driving roller 1 is pressed against second and third rollers 2 and 3. A pair of shoot guides 4 and 5 oriented upwards are provided above the nip (B) between first and second rollers 1 and 2 and the nip (C) between first and third rollers 1 and 3, respectively. In this geometry, a sheet A is fed through the nip (B) into the pocket formed between the pair of shoot guides 4 and 5 to be held therebetween. Then, the rear end of sheet A is moved along the peripheral surface of first roller 1 so that it is caught at the nip (C) and delivered out through the nip, thus inverting sheet A.
There is another configuration as shown in FIG. 2. In this case, first, second and third rollers 1, 2 and 3 are arranged in a vertical configuration. A pair of shoot guides 4 and 5 are disposed horizontally, and a stopper 6 is provided at a position corresponding to the size of sheet A. In this geometry, sheet A is fed through the nip (B) into the pocket formed between the pair of shoot guides 4 and 5 to be held therebetween. Then, the rear end of sheet A is moved along the peripheral surface of first roller 1 so that it is caught at the nip (C) and delivered out through the nip, thus inverting sheet A.
The copy rate of a copier (the number of copies produced per min) is determined by the sheet feed speed and the sheet interval. If the sheet feed speed cannot be increased due to process requirements, the only thing which can be done for enhancing the copy rate is to shorten the sheet interval. In the case where the sheet interval is reduced, whilst one sheet is sent out from the sheet inverting device, the next sheet is fed into the sheet inverting device. As a result, two sheets pass each other inside the sheet inverting device. In such a case, the apparatus suffered from a problem in that the second sheet may touch the first sheet to be inverted and tends to roll up it causing paper jam.
Conventional apparatuses further suffered from a problem in that when a large sized sheet or a thin type sheet is conveyed into the shoot, the sheet tends to be attracted to the interior wall of the shoot due to electrostatic force, etc., thus the conveyance of the sheet is prevented causing paper jamming.